Be more careful about when to do dynamic stack realignment. Since we have an

option to disable base pointer usage, pay attention to it when deciding
if we can realign (if no base pointer and VLAs, we can't).

llvm-svn: 113366

1 files changed, 9 insertions, 2 deletions

diff --git a/llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp b/llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp
index b153b68eb9b..7b4086875cc 100644
--- a/llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp
@@ -667,8 +667,14 @@ bool ARMBaseRegisterInfo::hasBasePointer(const MachineFunction &MF) const {
 }
 
 bool ARMBaseRegisterInfo::canRealignStack(const MachineFunction &MF) const {
+  const MachineFrameInfo *MFI = MF.getFrameInfo();
   const ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
-  return (RealignStack && !AFI->isThumb1OnlyFunction());
+  // We can't realign the stack if:
+  // 1. Dynamic stack realignment is explicitly disabled,
+  // 2. This is a Thumb1 function (it's not useful, so we don't bother), or
+  // 3. There are VLAs in the function and the base pointer is disabled.
+  return (RealignStack && !AFI->isThumb1OnlyFunction() &&
+          (!MFI->hasVarSizedObjects() || EnableBasePointer));
 }
 
 bool ARMBaseRegisterInfo::
@@ -1890,7 +1896,8 @@ emitPrologue(MachineFunction &MF) const {
   AFI->setGPRCalleeSavedArea2Size(GPRCS2Size);
   AFI->setDPRCalleeSavedAreaSize(DPRCSSize);
 
-  // If we need dynamic stack realignment, do it here.
+  // If we need dynamic stack realignment, do it here. Be paranoid and make
+  // sure if we also have VLAs, we have a base pointer for frame access.
   if (needsStackRealignment(MF)) {
     unsigned MaxAlign = MFI->getMaxAlignment();
     assert (!AFI->isThumb1OnlyFunction());